“We are not aware of an imminent threat,” said Denver water commissioner Penfield Tate. “But in the last several months, we’ve grown far more concerned about the vulnerability of the dam and the potential for catastrophic consequences downstream if the dam were targeted.”
The closure drew immediate fire from local officials, who were not given any advance warning.
Yes, there is a threat. My dad was preparing reports concerning similar terrorist threats when he was a civil engineering professor at Georgia Tech in the 1970s. But, this isn't a problem that required precipitous action with widespread collateral consequences including the impairment of ambulance services in the area.
Catastrophic, but extremely unlikely risks need to be weighed against small but significant high probability harms as a result of efforts to abate the unlikely risks. This comparison, moreover, needs to be conducted cautiously. The likely harms are usually possible to determine with some certainty. The unlikely harms are highly sensitive to the methodology used to assess them. Care is even more in order when the person making the decision, in this case, Denver Water, would be harmed by the unlikely risk, but not by the more probable harms flowing from the abatement efforts (reduced ambulance services and local economic impacts due to the closing of one of three main transportation arteries in the area).
Indeed, in a fair risk analysis, it would appear that the greater threat is not destruction of the massive earthen dam itself, potentially causing a catastrophic flood, but contamination of the water in the reservoir with a highly toxic substance, which is something that can be accomplished from many places other than the dam road at any large reservoir. If one is going to try to abate a low probability risk, one ought to do something that will really solve the problem, not simply engage in security theater.
Denver Water is, however, doing an excellent job at the core mission of managing Denver's water resources, a key element of which is a focus on water conservation. Via Westword, "water use in 2007 was 20 percent lower than 2001 use levels."
This game changing reduction in water use (equivalent in impact to Aurora, Colorado completely disappearing off the metropolitan area map) has taken place against a backdrop of urban growth, not decline. Also notable is the fact that Denver Water achieved this change with P.R., rather modest fines and regulations, and rather modest financial incentives to invest in water conservation. Once the public was made aware that we needed to conserve and we were told how to do so, the reaction was voluntary and heart felt. The public has taken action mostly as matter of moral imperative, rather than due to economic incentives.